I suspect the FP hull designs are very similar to the Manta, CS, Maine cat, and other "displanning" hull forms as Pete Brady would call them. These hull forms are very efficient in the displacement mode and the mid range 15-18 knots semi-displacement mode. Adding more horsepower after a point doesn't seem to add much more speed nor efficiency. I think some people don't understand the distinction of difference between these hull designs and full planning hull forms (symmetrical and asymmetrical). All out planning hull forms actually become more efficient at the higher speeds than the displacement type hulls, but don't enjoy the low speed efficiency, sea-kindliness, and fuel economy in the mid range of the displacement type hull forms. The Manta is a good example. With a pair of D-3 160 hp engines top end is 19 knots, with the D-4 225 hp 21 knots, with the 250 hp 23 knots. Based on overall efficiency, noise, etc we found the 225 hp to be well suited. At 75% throttle the 160 would cruise at 15 knots, the 225 at 17 knots and the 250 19 knots. I think FP is probably giving good advice about hp increases.

Dear Pat Thank you for your very detailed analysis. Generaly i agree but i cannot understand in the case of Manta cat how is possible from 160hp to 225hp to gain only 2kn (19-21kn) while from 225hp to 250hp (total increase 50hp instead of 130hp) gainning 2kn as well (21-23kn). Alexander ----- Original Message ----- From: "Pat Reischmann" <preischmann@msn.com> To: "power-catamaran" <power-catamaran@lists.samurai.com> Sent: Monday, January 07, 2008 4:02 PM Subject: [PCW] FP horsepower increase > I suspect the FP hull designs are very similar to the Manta, CS, Maine cat, > and other "displanning" hull forms as Pete Brady would call them. These hull > forms are very efficient in the displacement mode and the mid range 15-18 > knots semi-displacement mode. Adding more horsepower after a point doesn't > seem to add much more speed nor efficiency. I think some people don't > understand the distinction of difference between these hull designs and full > planning hull forms (symmetrical and asymmetrical). > All out planning hull forms actually become more efficient at the higher > speeds than the displacement type hulls, but don't enjoy the low speed > efficiency, sea-kindliness, and fuel economy in the mid range of the > displacement type hull forms. The Manta is a good example. With a pair of D-3 > 160 hp engines top end is 19 knots, with the D-4 225 hp 21 knots, with the 250 > hp 23 knots. > Based on overall efficiency, noise, etc we found the 225 hp to be well suited. > At 75% throttle the 160 would cruise at 15 knots, > the 225 at 17 knots and the 250 19 knots. I think FP is probably giving good > advice about hp increases. > _______________________________________________ > Power-Catamaran Mailing List